docs: def print_usage():
      """
          Prints usage message.
      """
  
      print('Usage: ' + os.path.basename(sys.argv[0]) + ' [options] dimacs-file')
      print('Options:')
      print('        -h, --help       Show this message')
      print('        -m, --model      Print model')
      print('        -s, --solver     SAT solver to use')
      print('                         Available values: g3, g4, m22, mgh (default = g4)')
      print('        -v, --verbose    Be verbose')